1. Field of the Invention
The present invention relates to an image recording material which can be used as a planographic printing plate. More particularly, the present invention relates to a negative type image recording material which can be used as a so-called directly producable planographic printing plate on which direct production by using an infrared laser based on digital signals output from a computer or the like is possible.
2. Description of the Related Art
Conventionally, as systems for producing a planographic printing plate directly from digital computer data, there have been proposed (1) a system using an electrophotographic method; (2) a system using a photopolymerizable compound, which is polymerized through exposure by a laser which emits blue or green light; (3) a system using a recording material in which a silver salt is laminated on a photosensitive resin; and (4) a system using a silver salt diffusion transfer method; as well as other methods.
However, the above system (1) using an electrophotographic method has complicated image formation processes such as charging, exposure, developing and the like, and thus, the apparatus for implementing this system becomes complicated and large. In system (2) using a photopolymerizable compound, since a planographic printing plate which is highly sensitive to blue or green light is used, it is difficult to handle in an illuminated room. In methods (3) and (4), since a silver salt is used, there are the disadvantages that processes such as developing and the like become complicated and the waste water naturally contains silver.
In recent years, laser technologies have developed remarkably. In particular, high output and compact solid-state lasers and semiconductor lasers emitting infrared rays of wavelengths of 760 nm to 1,200 nm are readily available. These lasers are very useful as a light source for recording in the direct production of a planographic printing plate from digital data such as digital computer data. However, since most photosensitive recording materials which are useful in practice are sensitive to visible light having wavelengths of 760 nm or less, image recording cannot be carried out with these infrared lasers. Therefore, a material which can be recorded with an infrared laser is desired.
Examples of such image recording materials on which images can be recorded with infrared ray lasers include a recording material comprising an onium salt, a resol resin, a novolak resin, and an infrared ray absorbing agent as disclosed in Japanese Patent Application Laid-Open (JP-A) No. 7-20629. Particularly, an image recording material using a diazonium salt as the onium salt has the merits that sensitivity is excellent in view of management and efficiency, and the material is relatively inexpensive. However, since the diazonium salt is highly reactive, there is the disadvantage that when the diazonium salt is used in an image recording material, the storability is not sufficient.